1. Technical Field
The present invention relates to an ultra compact valve unit for regulating pressure and to a liquid ejection device provided with such a valve unit.
2. Related Art
A liquid ejection device includes an inkjet-type printer (hereinafter referred to as a “printer”). Printers are provided with replaceable ink cartridges (hereinafter referred to as a “cartridge”). A printer accomplishes printing by ejecting (discharging) ink, which is supplied by a cartridge, from a recording head. There are several conventional methods for supplying ink from a cartridge to a recording head. The pressure on the ink must be suitably regulated so as to stably discharge ink droplets from the recording head. Therefore, printers include a valve unit (differential pressure valve or pressure reducing valve) to regulate ink pressure according to the ink supplying method used.
JP-T-2000-03877 discloses a differential valve built into a cartridge. This cartridge is mounted on a carriage and referred to as an on-carriage cartridge.
JP-A-2001-199080 discloses a carriage provided with a sub tank. The sub-tank recording device detects the amount of ink in accordance with the intensity of the magnetic line of force of a permanent magnet that varies depending on the floating position of a float member by means of electromagnetic conversion element such as a Hall element arranged on a side wall of the sub tank. The ink supply valve opens when the amount of detected ink is less than a predetermined amount.
JP-T-2003-041964 discloses a recording device including a main body provided with a cartridge holder. In this recording device, a cartridge is installed in the cartridge holder on the main body, and a valve unit is mounted on the cartridge. This kind of cartridge is referred to as an off-carriage cartridge.
JP-A-2005-186344 discloses a valve unit provided with a pressure reducing valve that reduces the pressure of a liquid within a pressure chamber containing liquid to a predetermined pressure. This pressure reducing valve is provided with a pressure receiving member that is elastically deformable, a spring used for pressure regulation, and an operating lever and the like. Therefore, the valve unit is large.
Whatever the type, conventional valves are large. Thus, a problem arises when developing compact and portable printers, since a corresponding compact valve unit is not available. The ink supplied to the recording head is regulated to a suitable ink pressure. Conventionally, valve units that regulate ink pressure differ according to the method in which ink is supplied. Therefore, it has been difficult to design a valve unit that would be commonly usable among recording devices that use different ink supplying methods. For example, if an ink pressure regulating valve unit could be built into a recording head, the valve unit could be used commonly among recording devices that employ different methods for supplying ink. However, the recording head would be enlarged since conventional valve units have a large structure. Therefore, there has not been as yet in fact a valve unit that could be built into a recording head.
Furthermore, the outer packaging member (case and the like) of a conventional valve unit is readily permeable to gas since it is typically formed of resin. Thus, the liquid content of the ink within the cartridge may evaporate, and gas that penetrates the interior of the cartridge produces bubbles in the ink. Therefore, the problem of gas permeability that causes moisture evaporation and bubbles must be reduced in such valve units.